This application is based on and claims priority on Japanese patent application 2001-161999, filed on May 30, 2001, the whole contents of which are incorporated herein by reference.
A) Field of the Invention
The present invention relates to a semiconductor device manufacture method and a reticle set for semiconductor device manufacture, and more particularly to a semiconductor device manufacture method in which one layer is exposed by using a plurality of reticles, and to a reticle set for such exposure.
B) Description of the Related Art
With the recent development of fine patterning of semiconductor integrated circuit devices, it becomes necessary to form fine wiring lines disposed at a minute pitch. In order to form such fine wiring lines, techniques have been introduced which expose one wiring layer by using a plurality of reticles. Such techniques known to date are, for example, phase edge techniques for shortening a gate length, techniques for forming a fine pitch pattern by exposing a double pitch pattern twice by displacing it by a half pitch, and the like.
A conventional process of forming one wiring layer by using a plurality of reticles will be described. A thin film is first formed on the surface of a semiconductor wafer, and photoresist is coated on this thin film. The position of a first reticle is aligned with the wafer, and then the resist film on the wafer is exposed by using the reticle to transfer a reticle pattern. Similarly, the second and following reticle patterns are transferred.
After the patterns of all reticles are transferred, a development process is performed to form a resist pattern. After the development process, a surface test, a pattern size test and a reticle position alignment test are executed. In the pattern size test, the pattern size of each reticle is compared with a reference size. In accordance with this comparison results, it is checked whether the pattern of each reticle was transferred under the proper exposure and focus conditions.
In the position alignment test, a placement error between an overlay measurement mark formed on the underlying layer and an overlay measurement mark formed on the resist pattern and a placement error between resist patterns transferred by different reticles are measured to thereby check whether a position alignment with the underlying pattern and a position alignment of patterns in the same layer are proper.
There is a variation in proper exposure amounts of a plurality of reticles to be used. For example, a proper exposure amount is different for each type of masks such as a halftone phase shift mask, a binary mask and a Levenson type phase shift mask. A proper exposure amount also changes with the value of "sgr" and the optical conditions such as oblique incidence illumination. A proper exposure amount also changes with the purpose of a mask, such as a main mask used mainly for forming a pattern and an auxiliary mask having a role of assisting the main mask.
Some reticles have a proper exposure amount smaller than a threshold value necessary for developing a resist film. When such a reticle is used, an alignment mark or overlay measurement mark cannot be resolved. An alignment mark is a mark used as a position alignment reference when an upper level wiring layer is formed. An overlay measurement mark is a mark used for testing a placement error between the pattern transferred by the reticle and a pattern of the underlying layer, same layer or upper layer.
A pattern transferred by a reticle having a lower proper exposure amount cannot be aligned directly with an upper pattern, because an alignment mark cannot be formed. Since an overlay measurement mark cannot be formed, it is not possible to test whether there is a placement error between a pattern transferred by a reticle having a lower proper exposure amount and another pattern.
It is an object of the present invention to provide a semiconductor device manufacture method capable of forming an alignment mark and an overlay measurement mark even if a reticle having a lower proper exposure amount is used.
It is another object of the invention to provide a reticle set to be used for such a semiconductor device manufacture method.
According to one aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: a first exposure step of exposing a partial area of a resist film formed on a surface of a substrate to light having a first intensity, first and second areas being defined on the surface of the substrate, the partial area being above the first area, and the light having the first intensity having transmitted through an area on a first reticle where a pattern to be transferred is formed; a second exposure step of exposing the resist film above the second area of the substrate to light having a second intensity weaker than the first intensity; a third exposure step of exposing the resist film above the first and second areas to light having a third intensity weaker than the first intensity, the light having the third intensity having transmitted through an area of a second reticle where a pattern to be transferred is formed; and a developing step of developing the resist film exposed.
In the second exposure step, an exposure amount of the resist film is increased. When a pattern is transferred to the area where the exposure amount is increased, the transferred pattern can be resolved.
According to another aspect of the present invention, there is provided a reticle set for semiconductor device manufacture, comprising: first and second reticles for exposing one layer formed on a substrate having a plurality of sections defined on a surface of the substrate, each section being exposed by one shot, an outer peripheral area of each section overlapping an outer peripheral area of a section adjacent to the first-mentioned section, this overlap area corresponding to a scribe line; and wherein: when a first section among first and second sections adjacent to each other is exposed, each of mark areas of the first and second reticles corresponds to the scribe line corresponding to the overlap area of the first and second sections, when the second section is exposed, each of margin areas of the first and second reticles corresponds to the scribe line corresponding to the overlap area of the first and second sections; a fifth mark is disposed in the mark area of the second reticle; and an area of the mark area of the first reticle corresponding to an area including a pattern transferred from the fifth mark on the substrate is a partial transmission area for partially transmitting exposure light.
When exposure is performed by using the first reticle, the resist film is exposed to light whose intensity was weakened by transmitting through the partial transmission area in the mark area. This exposure increases the exposure amount. It is therefore possible to obtain an exposure amount sufficient for resolving the fourth mark of the second reticle.
According to another aspect of the present invention, there is provided a reticle set for semiconductor device manufacture, comprising: first and second reticles for exposing one layer formed on a substrate having a plurality of sections defined on a surface of the substrate, each section being exposed by one shot, an outer peripheral area of each section overlapping an outer peripheral area of a section adjacent to the first-mentioned section, this overlap area corresponding to a scribe line; and wherein: when a first section among first and second sections adjacent to each other is exposed, each of mark areas of the first and second reticles corresponds to the scribe line corresponding to the overlap area of the first and second sections, when the second section is exposed, each of margin areas of the first and second reticles corresponds to the scribe line corresponding to the overlap area of the first and second sections; a seventh mark is disposed in the mark area of the second reticle; and an area of the margin area of the first reticle corresponding to an area including a pattern, on the substrate, transferred from the seventh mark is a partial transmission area for partially transmitting exposure light.
When exposure is performed by using the first reticle, the resist film is exposed to light whose intensity was weakened by transmitting through the partial transmission area in the margin area. This exposure increases the exposure amount. It is therefore possible to obtain an exposure amount sufficient for resolving the seventh mark of the second reticle.
According to another aspect of the present invention, there is provided a reticle set for semiconductor device manufacture, comprising: first and second reticles for exposing a resist layer formed on a surface of a substrate having a plurality of sections defined on the surface of the substrate, each section being exposed by one shot, an outer peripheral area of each section overlapping an outer peripheral area of a section adjacent to the first-mentioned section, this overlap area corresponding to a scribe line; and wherein: when a first section among first and second sections adjacent to each other is exposed, each of mark areas of the first and second reticles corresponds to the scribe line corresponding to the overlap area of the first and second sections, when the second section is exposed, each of margin areas of the first and second reticles corresponds to the scribe line corresponding to the overlap area of the first and second sections; said first reticle is formed with a pattern for exposing the resist film to light having an intensity supplying an exposure amount equal to or larger than a threshold level of developing the resist film, and said second reticle is being formed with a pattern for exposing the resist film to light having an intensity supplying an exposure amount lower than the threshold level; and an eighth mark is disposed in the mark area of said second reticle, and an area of the margin area corresponding to an area including a pattern, on the substrate, transferred from the eighth mark is a partial transmission area for partially transmitting exposure light.
Since the resist mask is exposed to light having transmitted through the margin area of the second reticle, the exposure amount is increased. It is therefore possible to obtain an exposure amount sufficient for resolving the eighth mark of the second reticle.
As above, since the total exposure amount is increased, an alignment mark or overlay measurement mark can be transferred by using a reticle which is used under the condition of an exposure amount lower than the development threshold value.